Electric phonograph reproducer



y 1 3 A. A. THOMAS 1,958,386

ELECTRIC PHONOGRAPH REPRODUCER Filed'vJan. 25, 1929 2 Sheets-Sheet 1 y 8, 1934. A. A. THOMAS 1,958,386

ELECTRIC PHONOGRAPH REPRODUCER Filed Jan. 25, 1929 2 Sheets-Sheet 2 4 lmnum INVENTOR WA m I Patented May 8, 1934 UNETED STATES 'i; .QFFICE 10 Claims.

This invention relates to the art of reproducing recorded sound, and its object is to provide an electromagnetic phonograph reproducer of novel construction and improved operation. The main feature of my instrument in its preferred form comprises an armature bar pivoted at the center on a twistable spring shaft which carries a stylus holder for playing lateral-cut or vertical-cut records. The ends of the armature bar cooperate with two pairs of magnet poles to vary the flux through one or two coils surrounding the armature. The arrangement is such that the armature is normally balanced, not only mechanically by the supporting spring shaft, but also magnetically by the poles of the field magnet. Since the movements of the stylus point are transmitted to the center of the armature in the form of lateral oscillations, these movements are greatly amplified at the two ends of the armature. Consequently, the minutest vibrations of the stylus point are multiplied at the armature ends to generate current impulses of appreciable strength, and these impulses may be amplified as required to operate loudspeaker mechanism.

My new electric pickup may also have a stylus for playing vertical-cut records without adjusting the device on its supporting arm. For this purpose it is only necessary to attach a vertically movable stylus member to one end of the centrally pivoted armature bar. The needle holder for lateral-cut records and the stylus member for vertical-cut records project through the bottom of the casing in substantially parallel relation. The arrangement of these two stylus memhers is such that neither interferes with the operation of the other, and the device is always in condition to play either type of record without adjustment.

The foregoing and other novel features and practical advantages of my invention will be clearly understood from a detailed description of the accompanying drawings, in which- Fig. 1 shows an inside view of an electric phonograph reproducer constructed in accordance with my invention;

Fig. 2 is a transverse sectionon line 2--2 of Fig. 1;

Fig. 3 is a view similar to Fig. 1, except that certain parts are in section for clearness;

Fig. 4 is a transverse section on line i-4 of Fig. 1;

Fig. 5 presents a plan view of the instrument, partly in section and partly broken away for clearness Fig. 6 is a fragmentary plan view, approxi- (Cl. I'm-4.00.41)

mately on line 6-6 of Fig. 3, to show the form and mounting of one of the pole pieces;

Fig. '7, which is a fragmentary view similar to Fig. 4, illustrates a slightly modified form of stirrup to which the needle holder is attached;

Fig. 8 shows an inside face view of a modification employing two semi-circular magnets in place of the single U-shaped magnet of Fig. 1;

Fig. 9 represents a transverse section on line 99 of Fig. 8;

Fig. 10 is a view similar to Fig. 8, except that certain parts of it are sectioned along the line 10-10 of Fig. 9;

Fig. 11 is a sectional plan view on line 1111 of Fig. 8;

Fig. 12 illustrates the armature bar and its supporting spring blade in separated position;

Fig. 13 shows the armature mounted on the spring blade, the latter being in section; and

Fig. 14 illustrates diagrammatically aconstruction in which the armature is arranged vertically and operated by a stylus member playing vertical-cut records.

Before taking up a detailed description of the various figures, I wishto explain that the drawings have been enlarged to make them clear and easy to read. v The parts have been purposely spread out more than necessary and their relative proportions have been exaggerated. It will therefore be understood that the drawings are not to be regarded as drawn to scale with mathematical accuracy. The actual instrument is considerably smaller and more compact than the drawings indicate.

Referring to Figs. 1-6, there is a casing 10 provided with a hub 12 for mounting it in operative position on an arm 13 pivoted to swing horizontally over a record on the turntable. The arm 13 is also capable of vertical movement, as is usual in phonographs. This will be understood without additional illustration, particularly since mountings for reproducer arms are well known in the trade. The casing 10 in this instance comprises a main body part 14 of U-shaped outline, a back plate 15 and a front plate or cover 16. The main part 14 of the casing is formed with bosses 1'7 having holes '18 for receiving screws 19 to attach the back and front plates 15 and 16 in position. If desired, the back plate 15 may be cast or molded integral with the body portion 14. The hub 12 may be formed integral with plate 15 or secured thereto as a separate piece. The casing 10 may be constructed of sheet metal, preferably aluminum, which is light and strong, or it may be molded of suitable composition material,

j center with a rectangular hole 40.

such as bakelite. A set-screw 20 or the like secures the casing in proper position on the supporting arm 13.

A U-shaped permanent magnet 21 is secured to the back plate 15 by suitable means, such as screws or rivets 22. The casing part 14 and magnet 21 are shaped alike, so that a magnet of maximum length may be mounted in the casing. This magnet may be solid or laminated, and a good material to use is cobalt steel. The magnet 21 carries a pair of pole pieces 23 and 24. Each pole piece has a lateral extension 25 in contact with the adjacent end of the magnet. Fastening members 26, which may be screws, bolts, or rivets, pass through the magnet and extensions 25 to secure the pole pieces rigidly to the magnet. The upper pole piece 23 terminates in a pair of downwardly extending projections 27 and 28, and the lower pole piece 24 has a pair of similar projections 29 and 30 extending upwardly toward the other pair of polar'projections. The two pairs of oppositely arranged polar projections 27-29 and 2830 are separated by airgaps 31 and 32, as best shown in Fig. 3. These polar projections are preferably (but not necessarily) tapered to intensify the magnetic flux across the airgaps. If we assume the field magnet 21 to have the polarity indicated in Fig. 3 by the letters N and S, the polar projections 27 and 23 are north poles, while the polar projections 29 and 30 are south poles, so that the field flux passes across the airgaps 31 and 32 in parallel paths. The pole pieces 23 and 24 may be solid or laminated, and are preferably constructed of silicon steel or other metal having a higher magnetic permeability than the field magnet. Each pole piece is easily stamped and shaped from a single piece of metal.

A non-magnetic U-shaped bracket 33 is secured to the back plate 15 by bolts, screws or rivets 34. This bracket is arranged substantially horizontal and extends across the width of the casing to the cover 16. If desired, the bracket 33 may be secured to the cover 16 by screws 35 to support the bracket at the front and rear for greater rigidity. In that event, the screws 35 must be taken out for removal of the cover 16, but that will not disturb the bracket, because it is supported independently of the cover. The bracket 33 may be stamped or cast as a single pieceof aluminum, or other material having the requisite strength and being preferably light in weight. The two arms of bracket 33 are provided with a pair of aligned slots 36 for receiving the ends of a resilient shaft 37 in a tight fit. This shaft is here shown as a blade or band of spring metal, but it may obviously be of other shape, provided it has the requisite strength and resiliency. By forcing the ends of the spring blade 37 into the slots 36, a rigid permanent connection is established without the need of additional fastening means. The spring blade 37 is laterally twistable at the center, and the supporting bracket 33 is cut away at 38 (see Fig. 5) to increase the effective length of the blade or shaft.

An armature bar 39 is centrally mounted on the center of spring blade 3'7. A simple way to connect these two parts is illustrated in Figs. 12 and 13. The spring blade 37 is provided at the In making this hole, the sides 41 are slotted beyond the top and bottom edges of the hole, as indicated at 43 in Fig. 12. The result is to form resilient tongues 44 adapted to snap into the transverse slots 45 in armature 39 when the latter i fo ced through hole 40 in the spring blade. The tongues 44 fit tightly in the slots 45, so that the armature bar is rigidly secured at the center to the center of the twistable spring blade 37. If desired, solder 46 or other additional securing means may be used to seal the connection between the armature 39 and spring blade 37. It is evident that these two parts constitute a single vibratory member. The ends of armature bar 39 extend into the air gaps 31 and 32. One or two coils 47 surround the armature 39, and they are securely held in place between the polar projections 23 and 24 by the U-shaped bracket 33. That is to say, the coils 47 are firmly held at the top and bottom between the pole pieces 23 and 24, while the frame 33 engages the coils back and front, whereby they are securely held in place without the need of additional fastening means. The coils 47, which can be machine-wound, are preferably comiected in series in a suitable reproducing circuit, as will be understood without further description.

A U-shaped frame or stirrup 48 is secured at its upper end to the twistable spring blade 37 on opposite sides of the armature 39, as best shown in Fig. 4. The ends of the stirrup or yoke arms 48 are slotted and forced into rigid engagement with the spring blade 37, so that the two parts are secured together without separate fastening means, although such may be used if desired. The stirrup 48 may consist of a fiat band of aluminum or other strong metal bent into U- shape, so that it can straddle the lower pole piece 24. A needle holder 49 is attached to the cross-piece 59 of stirrup 48 in any practical way, as by a screw, rivet, solder and the like. A slot 51 in the bottom of casing 10 permits the stirrup 48 to vibrate freely without striking the casing. In Fig. 4 the stirrup 48 is provided with parallel side arms, whereas in Fig. 7 the stirrup has side arms which converge at 48, so that the upper ends ofv the stirrup arms may engage the spring blade 37 nearer the armature 39. This arrangement makes it somewhat easier to oscillate the spring blade by the lateral vibrations of the needle 52 in holder 49. The latter may be slanted forwardly to hold the needle at the desired trailing angle, or the same result may be accomplished by mounting the casing at an angle on its supporting arm.

To facilitate assembling of the parts, the stirrup 43 is made sufiiciently long to permit insertion oi. the lower'pole piece 24 between the crosspiece 50 of the stirrup and the bottom of the coil or coils 47. This will be understood by looking at Fig. 3. It goes without saying that the parts are assembled outside of casing 10, so that the entire mechanism can be inserted as a unit into the casing.

The operation of the instrument above described will'be apparent from Fig. 3, and it is enough to say that the lateral vibrations of needle 52 oscillate the twistable spring shaft 37 and thereby rock the armature bar 39 to vary the magnetic flux through the coil or coils 47. This will be understood by those skilled in the art without the need of elaboration. It should be particularly noted that the movements of the needle point are transmitted to the armature ends in greatly amplified ratio, whereby the efiiciency of the instrument is correspondingly increased. This makes it possible to play the new style of records in which the needle track runs to several hundred lines per inch. The micro scopic movements of needle 52 are sufficient to Vibrate the ends of armature 39 to such a degree circuits are well known irrthe art-and' form nosilient shaft 37, and magnetically by 'the field flux in the-airgaps-Bl and 32'. Since the needle 52 is substantially in vertical alignment withthe spring blade 37, which is mounted edge-wise in avertical plane, it is eVident' that this shaft easily supports-the entire weight of the -reproeducer; The material, shape anddimensions of spring shaft 37 are so chosen that ithas the-right. amount of resi-liencyzand offers the proper degreeof resistance or mechanicalload'to the move ments of the stylus. These factors can-be readiliy= determined by experiment welrwithintheskill of the artisan in this particularline.

The electric pickup abovedescribedmay also be-used for playing-vertical-cut records byat= taching a stylus member 53'to an extension-54. of armature bar 39. The upper end of'stylus member 53 may be slotted to receive'the'armature extension and the parts may be-rigidly connected in any practical way, as by solder, welding, riveting, and so forth. The stylus member 53 may simply be ail-aluminum pin bevelled at itslower end andcarrying a stylus point 55 adapted to play vertical-cut records. For rec ords of the Edisontype, the stylus point 55 isusually a diamond point permanently attached; It is clear from Fig. 3 thattheverticalmovements of stylus member 53 rock the armature bar 39 about the twistable spring blade 37; The stylus member 53 projects through a-hcle or slot 56 in the bottom of casing 10. When the pickup plays lateral-cut recordsby' means of the 'needle- 52, the stylus point 55 remains above the surface of the record and-istherefore not in the way. Likewise, when the stylus 55 is in playing position on a vertical-cut record, the lower edge 5'7 of the needle holder 49 is above the surface of the record. Since the movements of the armature bar 39 are very small, even at maximum amplitude, small pieces of rubber may be inserted in the airgaps between the armature and the adjacent polar faces. Such elastic pads perform the double function of damping the armature movements and preventing the armature ends from striking the adjacent pole faces. The use of such pads, however, is not ordinarily required, because the spring shaft 37 damps the armature movements by always tending to return it to normal position, and the resisting strength of this shaft is sufficient to keep the armature ends from striking the pole pieces.

In the modification of Figs. 8-11, the field magnet structure comprises a pair of U-shaped or 1 semi-circular magnets 58 secured by suitable fas tion. The permanent magnets 58 terminate in lateral polar extensions 62 and 63. If the extensions 62 are assumed to be north poles, the extensions 63 are south poles. The north poles 62 are connected by a pair of pole pieces 64 and 65, which terminate in polar projections 66 and 6-7'; respectively. The south poles 63 of the magnets --are connected by polepieces '63 and 69;- which end in polar projections 70 and-715 It is clear from this that the; two-magnets 58 with their. pole pieces constituteein eifect a single magnet of increased lengtln The two pairsof? oppositely arranged polar projections 66-----"70""and* 6 7 -71 provide two airgaps which I have indi cateduby the-numeralsBl and 32, because they. are identical with the airgaps 31 and 32in Fig. 3;. The'pole-pieces' 64; 65, 68- and 69 are attached to the.- lateral extensions-62 and 63 by bolts or screws '72, which holdthe parts in intimate magnetic contact with each other. Since the other. parts. of Figs. 6 l1- are substantially identical with-the construction shown .in'Figs; l--5; itwill notbe necessary to repeat the detailed description of the first construction for the modification shown in Figs.-8ll. For" this reason I'thillkit. is sufiicient toindicate' corresponding parts.=.in the-two constructions by the same-reference nu:-. A merals; What has-been said for-the operation.- ofF'igszl-5'holds' good for Figs. 8-11. vent unnecessary: duplication, Ihave omitted the vertically movable stylus member 53ffrom Figs. 8 11, but'Iwant it understoodfthat the armae ture 39 in Figs. 8-11 may carry the stylusmember' 53 .for 'playing vertical-cut records,

If my new pickup is to be used for" playing vertical-cut records only, the arrangement illustrated-in Fig. 14 maybe used, where the armature 39 is arranged vertically and-the stirrup 48 horizontally. In other words, those twoparts are now arranged in a positionat right angles to their position in the preceding figures.- Locke ing at Fig. 14, it is clear that the vertical 'movements of the stylus member-53oscillate the ar mature-bar 39 laterally about the twistable spring b1ade37to generate currentimpulsesin the-coil or coils 47.

Although I have shown and described certain specific constructions, I" want it clearly understood that my inventionis not limited"to the details set forth; Changes and modifications may bemade by those skilled' 'in the art'without de--- parting from the scope of the invention as defined in the appended claims.

I claim as my invention:

1. An electric phonograph reproducer comprising a spring blade rigidly supported at its ends and laterally twistable at the center, an armature bar secured at the center to the center of said spring blade, a stirrup attached to said spring blade on opposite sides of said armature bar, a stylus holder carried by said stirrup, and electromagnetic means for converting the movements of said armature bar into electric impulses.

2. In an electric phonograph reproducer for playing lateral-cut records and vertical-cut records, the combination of a pivoted armature bar, means connected to the pivot of said bar for operating the same when playing one of said types of record, means connected to one end of said bar for operating the same when playing the other type of record, and electromagnetic means for converting the movements of said armature bar into electric impulses for either type of record.

3. An electric phonograph pickup comprising a centrally pivoted armature bar, a laterally movable stylus holder connected to the center of said bar for oscillating the same when playing lateralcut records, a vertically movable stylus holder connected to one end of said bar for oscillating the same when playing vertical-cut records, and

To pre- 7 electromagnetic means for converting the inovements of said armature bar into electric impulses when playing either type of record.

4. An electric phonograph reproducer comprising a magnet having two pairs of polar projections forming two aligned airgaps, a twistable spring shaft supported at its ends and arranged transversely between said polar projections, an armature connected at the center to said spring shaft and having its ends extending into said airgaps, a coil surrounding said armature, a stirrup connected to said spring shaft on opposite sides of the armature, and a stylus holder. attached to said stirrup. r

5. An electric phonograph reproducer comprising a magnet having two pairs of polar projections forming two aligned airgaps, an oscillatory shaft supported transversely between said polar projections, an armature mounted centrally on said shaft and having its ends extending into said airgaps, a coil surrounding said armature, a laterally movable stylus holder connected to said shaft for vibrating the armature when playing lateral-cut records, and a vertically movable stylus holder connected to one end of said armature for vibrating the same when playing vertical-cut records.

6. In an electric phonograph reproducer, a vibratory unit comprising a spring blade rigidly supported at its ends and laterally twistable at the center, a pair of resilient tongues at the center of said blade and spaced to provide an opening, an armature bar having a pair of transverse slots substantially at the center on opposite sides, said bar being adapted to pass through said opening until said tongues snap into said slots and lock the bar to the spring blade, whereby these two parts are rigidly connected, a stirrup attached'tov said spring blade on opposite sides of said armature bar, and a stylus holder carried by said stirrup.

7. An electric phonograph reproducer comprising a casing, a magnet mounted in said casing and having two pairs of polar projections arranged to form two aligned airgaps, a frame in said casing, said frame having a pair of spaced arms provided with two aligned slots, a laterally twistable spring blade supported at its ends in said slots, an armature connected at its center to the center of said spring blade and having its ends extending into said airgaps, a coil surrounding said armature, a stirrup connected to said spring blade on opposite sides of the armature, and a stylus holder attached to said stirrup.

8. An electric phonograph reproducer comprising a spring shaft rigidly supported at its ends and twistable at the center, an armature secured to the center of said shaft substantially at right angles thereto, a laterally movable stylus holder connected to said spring shaft for oscillating the same when playing lateral-cut records, a vertically movable stylus holder connected to one end of said armature for oscillating the same when playing vertical-cut records, said spring shaft holding the armature and stylus holdersin predetermined normal position, and electromagnetic means for converting the movements of said armature into electric impulses when playing either type of record.

9. In a phonographic device, the combination of an elongated suspension arm, a casing secured to one end of said arm and extending beyond the same, electro-magnetic sound-translating mecha-,

nism in said casing, said mechanism having a movable armature, and means in said casing for providing a short pivot axis for said armature lying substantially in a forward extension of the longitudinal axis of said arm.

10. In a phonographic device, the combination of an elongated suspension arm, a casing secured to one end of said arm and extending beyond the same, electromagnetic sound-translating mechanism in said casing, said mechanism having a movable armature, a short pivot shaft in said casing for operatively supporting said armature, and means for mounting said pivot shaft so that its axis lies substantially in a forward extension of the longitudinal axis of said arm.

ADOLPH A. THOMAS. 

